Process off-gas from a modified in situ oil shale retort using Anvil Points Mine (near Rifle. Colorado) shale was found to contain aluminum, boron, barium, calcium, copper, iron, potassium, lithium. manganese, magnesium, nickel, molybdenum, sodium, phosphorus. silica, strontium, vanadium, zinc, ammonia. hydrogen sulfide, and various hydrocarbon species. Cobalt. chromium, lead, antimony, selenium, and thorium were detected in the raw and spent shale but not in the gas emissions. The concentrations of metals, especially metal particulates, varied considerably during the course of the simulated in situ retorting test, which was performed in the Western Research Institute 10-ton oil shale retort at Laramie, Wyoming. Elemental closure was difficult to demonstrate because of the large variance in gas metal emissions during the course of the four-day test.